feat(trigger): add API endpoint to retrieve trigger plugin icons and enhance workflow response handling

- Introduced `TriggerProviderIconApi` to fetch icons for trigger plugins based on tenant and provider ID.
- Updated `WorkflowResponseConverter` to include trigger plugin icons in the response.
- Implemented `get_trigger_plugin_icon` method in `TriggerManager` for icon retrieval logic.
- Adjusted `Node` class to correctly set provider information for trigger plugins.
- Modified TypeScript types to accommodate new provider ID field in workflow nodes.

api/core/trigger/entities/entities.py

@@ -155,7 +155,8 @@ class TriggerProviderEntity(BaseModel):
         default_factory=list,
         description="The configuration schema stored in the subscription entity",
     )
-    subscription_constructor: SubscriptionConstructor = Field(
+    subscription_constructor: SubscriptionConstructor | None = Field(
+        default=None,
         description="The subscription constructor of the trigger provider",
     )
     events: list[EventEntity] = Field(default=[], description="The events of the trigger provider")